Regulation of naive T cell function by the NF-κB2 pathway

T cell activation involves the orchestration of several signaling pathways, including that of the 'classical' transcription factor NF-kappa B components NF-kappa B1-RelA. The function of the 'nonclassical' NF-kappa B2-RelB pathway is less clear, although T cells lacking components of this pathway have activation defects. Here we show that mice deficient in NF-kappa B-inducing kinase have a complex phenotype consisting of immunosuppression mediated by CD25-Foxp3-memory CD4(+) cells and, in the absence of those cells, hyper-responsive naive CD4(+) T cells, which caused autoimmune lesions after adoptive transfer into hosts deficient in recombination-activating genes. Biochemical studies indicated involvement of a cell-intrinsic mechanism in which NF-kappa B2 (p100) limits nuclear translocation of NF-kappa B1-RelA and thereby functions as a regulatory 'brake' for the activation of naive T cells.